US3696478A

US3696478A - Treatment of yarns

Info

Publication number: US3696478A
Application number: US889517A
Authority: US
Inventors: David Robert Elliott; John Michael Greenway
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1969-09-23
Filing date: 1969-12-31
Publication date: 1972-10-10
Anticipated expiration: 1989-10-10
Also published as: BR6915759D0; BE743983A; NL6919686A; FR2060464A5; ZA698977B; DE1965678A1; GB1290912A

Abstract

Yarn relax process wherein a yarn is tensioned and forwarded by means of an unheated fluid device to a hot zone wherein tension falls.

Description

United I States Patent Elliott et al. [451 Oct. 10, 1972 [54] TREATMENT OF YARNS [56] References Cited [72] Inventors: David Robert Elliott; John Michael UNITED STATES PATENTS Greenway, both .of Harrogate, England 2,242,988 5/1941 Avems ..28/72.l X 2,971,683 21961 P u] ..19159R X [731 Assignee Imperial chemical names 3 241 212 3/1966 Bi /mf al I 28/1 4 Limited London England 3,408,716 11/1968 Tradewell ..28/62 [22] Filed: Dec. 31, 1969 3,439,391 4/1969 12g Yg[ e t a1., ..,.,...28/62 X 21 pp NOJ 517 3,457,610 t ..28/1.4 3,478,401 11/1969 Whitworth et al ..28/62 3,526,024 9/1970 Fay ..28/62 [30] Foreign Application Priority Data Sept. 23, 1969 Great Britain ..46,828/69 Primary Examiner-Louis K. Rimrodt Attomey-Cushman, Darby & Cushman [52] US. Cl ..28/72.l 51 1m. 01. ..D02g 1/00 [57] ABSTRACT [58] Field of Search ..28/1.2,1.3,1.4, 72.1, 72.11,

28/7212, 217, 161/173 Yam relax process wherein a yarn is tensioned and forwarded by means of an unheated fluid device to a hot zone wherein tension falls.

14 Claims, 2 Drawing Figures TREATMENT OF YARNS This invention relates to the treatment of yarns and in particular to a method for the relaxation of continuous filamentary yarns composed of thermoplastic 5 polymeric material.

In the production of artificial or synthetic thermoplastic continuous filamentary yarns they are subjected to a drawing or stretching process under tension, following which it is usually required to relax the yarn partially or completely either to produce the desired physical properties, such as a reduced shrinkage propensity in the processed yarn or to produce some other effect, such as bulking or crimping of the filaments comprising the yarn when these have an inherent tendency to retract into a crimped form under low tension, optionally assisted by heat.

Hitherto such relaxation, has been carried out either by a batch process, wherein the yarn is temporarily collected in some form of package which allows a degree of contraction to take place or by continuously subjecting the running yarn to treatment with a hot fluid. These methods, in particular the latter one, suffer from the disadvantage that the yarn properties produced may fall short of the ideal particularly for materials subject to crystallization under the influence of heat.

Thus according to the present invention we provide a process for relaxing a running continuous filamentary 'yam composed of thermoplastic polymeric material, wherein the yarn is drawn from a supply means by entrainment in a fluid tensioning device supplied with an unheated gaseous fluid and is passed thereafter through a heating zone at a low, a substantially zero or a decreasing tension.

Yarn may be supplied to a fluid tensioning device in the present invention direct from the draw roll of a drawing machine or the dawn yarn may be temporarily packaged under tension from which package it is supplied to the fluid tensioning device by way of a tension gate or feed roll/nip roll combination. The former continuous method of operation is preferred.

Yarns composed of filaments of any thermoplastic polymeric material or materials may be relaxed in a process according to the present invention, as for example polyesters, polyamides, polyolefines or copolymers within or between these classes. The process is applied with particular advantage to yarns composed of materials which are not crystalline or are partially crystalline in the unrelaxed state and which are caused to crystallize or increase in crystallinity when heated. Treatment of such yarns by conventional relaxation methods would lead to the premature setting into the filaments of the physical properties possessed in the unrelaxed state by crystallisationand may well prevent or considerably reduce the improvement in" properties of a drawn yarn or the bulking effect in the case of an inherently retractable yarn. A process of the present invention, wherein a fluid tensioning device is supplied with an unheated gaseous fluid, effectively overcomes these disadvantages of known yarn relaxation processes.

Yarns composed of polyester or copolyester filaments, as for example, polyethylene terephthalate filaments are prone to crystallize when heated and may advantageously be relaxed by a process according to this invention.

Yarns composed of conjugate filaments that is of two or more components arranged in a contiguous fashion, either side-by-side or as a sheath and eccentric core, along the length of each filament, will have an inherent tendency to contract into crimped form on relaxation if the two components have a different shrinkage tendency. Such conjugate filament yarns may advantageously be relaxed in a process according to this invention.

Bulky conjugate filaments comprising two polyesters of different properties, as for example, different intrinsic viscosity or chemical composition having properties heretofore unknown in such polyester filaments may be produced by relaxation according to the present process particularly when a high temperature, that is a temperature of about 250C in the relaxation zone is used.

Thus according to another aspect of this invention we provide a crimped conjugate filament comprising two polyester components of the same chemical composition but different intrinsic viscosity and birefringence,'the intrinsic viscosity and birefringence of the components in the filament differing by at least 10 percent of the lower value and by at least 0.005 respectively, said filament having a retraction under load as hereinafter defined of at least 6 percent.

Methods for the production of crimpable conjugate filaments are described for example in United Kingdom Specification 1050042 and in particular in United Kingdom Specification 1157453 wherein polyester conjugate filaments are described.

Filaments having an inherent retraction tendency as do conjugate filaments may be produced by other methods, as for example assymmetric cooling or asymmetric heating and by false twisting processes and such filaments or filamentary yarns comprising them may be relaxed by the present process when a good bulk and crimping effect is obtained in a continuous process. United Kingdom Specification l028979 describes one such process of asymmetric heating.

In a process according to this invention an advantage may be obtained which is not possible by any other method of feeding a filament or yarn to the relax zone. This advantage derives from the fact that a lower feed tension is required in forwarding a yarn by a fluid tensioning device tan, for example, by a feed roll system and accordingly a greater relaxation effect may be achieved in the relax zone. This is a very tangible benefit in most relax processes for usually the inherent filament forces causing physical changes in the relax process are ve'ry small and easily interfered with by any extraneous tension.

A fluid tensioning device for carrying out a process according to this invention comprises an aspirator or ejector jet which may have any of several forms. One suchform comprises a yarn entry passageway or narrow bore into which yarn is drawn by the suction developed therein by entry into the passageway of an unheated gaseous fluid under pressure downstream of the point of entry of the yarn, said fluid proceeding through the passageway in a generally downstream direction. A fluid pressure is used such as to provide the required tension to draw the yarn from the supply means into the yarn passageway and forward it to a succeeding heating zone.

In another form of fluid tensioning device the yarn entry tube or passageway is quite short and its lower end is surrounded by the open end of a slightly larger tube. The junction of the 'two' tubes is enclosed in a chamber to which unheated gaseous fluid under pressure is supplied. The fluid enters the larger tube through the space between the two tubes and in passing through the larger tube induces a reduced pressure in the yarn passageway which draws a yarn thereinto tensioning and forwarding it through the larger tube to the heating zone.

One form of heating zone which may be used in a process according to this invention comprises an enclosure directly attached to the yarn exit passageway of the fluid tensioning device and of larger cross-section than said passageway into which the yarn is fed by means of a rotating tube having its exit directed outward towards a wall of the enclosure. The enclosure is heated by suitable means, as for example, a heated vapor jacket or electrical heaters mounted externally. By this means there is a drop in pressure and velocity of the fluid as it expands into the enclosure allowing the yarn to relax and fall through the heated atmosphere within the enclosure in a substantially tensionless state. In operating apparatus of this type to the best advantage it is preferred to cause the yarn to leave the rotating tube at a sufficient velocity to be carried across the gap between the end of the tube and a wall of the heated enclosure and to strike the wall thereof preferably at a glancing angle before continuing to fall through the heated atmosphere. This gap may be quite small, for example 3-5 mm. In this way the yarn takes a more stable and even, helical path through the heating zone and the relaxation process operates more effectively. The part of an enclosure wall contacted by the yarn takes a more stable and even, helical path through the heating zone and the relaxation process operates more effectively. The part of an enclosure wall contacted by the yarn should be smooth and free from irregularities which could snag the yarn and may be specially treated to produce a low friction, as for example covered .with a layer of polytetraflouroethylene. Alternative to the rotating yarn exit passageway a stationary tube directing the yarn at a glancing angle toward a wall of the enclosure may be used or a tube which oscillates to and fro causing the yarn to assume a zig-zag path through the heating zone.

In an alternative form of heating zone yarn issuing from a fluid tensioning device enters an externally heated passageway of steadily increasing cross-section.

. In the latter form a taper of not greater than is preferred. In apparatus of these forms the velocity and pressure of the entering fluid carrying a yarn either rapidly or steadily decrease allowing yarn tension to decay and relaxation under the influence of heat. The length of the heating zone is selected to allow the required amount of relaxation which is influenced by heating zone temperature. Threading up a fluid tensioning device with a running yarn which is handled by a temporary collecting means, as for example a suction gun,may be facilitating by providing a narrow longitudinal slot in the tensioning device and the relax zone.

Air is the most convenient fluid for use in this invention but other gases not having any harmful effect on thermoplastic polymeric substances may be used.

Alternative to externally heating the heating zone a slow coor counter-current flow of hot gas may be used instead provided care is taken to ensure that the relaxing yarn is not disturbed by the hot gas. In this case steam particularly dry steam may be used as the gas.

Yarn emerging from the heating zone is collected in any way which does not allow collecting tension to run back to the relaxation zone. For example a pair of rolls pressed into close contact with each other and preferably with one surface covered by a resilient material (that is, a roll/nip roll combination) may be used and by this means the amount of relaxation occurring may be controlled by adjusting the relative speeds of this roll combination and that of the supply of yarn to the relax process. The ratio of these speeds is usually referred to as the relax ratio.

Apparatus for carrying out the process of the invention is illustrated in the attached drawings wherein;

FIG. 1 illustrates in section relaxation apparatus wherein a countercurrent flow of hot air is used to effect relaxation of yarn fed in by means of a rotating tube.

FIG. 2 illustrates in section a relaxation apparatus wherein relaxation is effected in a uniformly divergent enclosure.

Referring to FIG. 1 a yarn tensioning device comprises a yarn entry tube 2 of narrow bore the open lower end of which is spaced a small distance from an exit passage 3 of a surrounding enclosure 4 to which unheated fluid under pressure is supplied at 5. Exit passage 3 is jointed by a swivel coupling 6 to a rotatable tube bent at its lower end towards a wall of a cylindrical enclosing vessel 8 of very much increased cross-section, the exit from tube 7 being arranged so as to direct issuing fluid in a direction parallel to a tangent to the vessel wall at the point of contact. A pulley 15 mounted at the upper end of tube 7 allows the tube to be rotated by suitable driving means (not shown). Vessel 8 is open at its lower end and closed at its upper end and except for an opening through which the tube 7 extends and two small slots 9 near the point of entry of the rotatable tube 7. Mounted around the lower end of vessel 8 is a hollow ring 10, the internal wall 11 of which is of sintered metal or other porous material of sufficient strength to which a conduit 12 for the supply of hot fluid is attached. Situated some distance below the open end of vessel 8 is a take-off roll 13 against which a rubber covered nip roll 14 is firmly pressed.

In operation of yarn 1 is drawn from a supply means (not shown) into the yarn entry tube 2 by the suction generated therein by passage of the compressed fluid from 5 passing into exit passage 3 through the small clearance between tube 2 and passage 3. The yarn forwarded by the fluid through the rotating tube 7 exits therefrom and impinges against the wall of vessel 8 falling in substantially uniform helical coils through the atmosphere of heated fluid in the enclosure 8 supplied from ring 10 in a steady upward current through the porous wall 1 1. The upward velocity of air is controlled at a low value by the pressure within ring 10 and the size of slots 9 which may be of adjustable opening. The relaxed yarn issuing from enclosure 8 may be allowed to cool by natural convection while passing to rolls 13/14 or by a forced current of cooling air applied after rolls 13/14 preferably in a manner which does not allow tension to develop in the yarn while it is still warm or hot. The relaxed yarn passes through the nip between rolls l3 and 14 to a conventional winding means (not shown) the winding tension being stopped at the nip.

Referring now to FIG. 2 a cylindrical casing 15 carries the parts of the apparatus in easily demountable form. A cap 16 spigotted into the upper end of casing 15 and retained in place by screws 17 carries symmetrically a number of holes 18 for entry of the working fluid. A yarn entry tube 19 is inserted through a central hole in cap 16 protruding some distance into the casing 15. Inside the casing 15 and spaced a small distance from the lower side of cap 16 by a spacing ring 20 is a diffusing plate 21, of, for example, sintered metal, through a bush 22 in which the exit end of the yarn tube 19 protrudes into a cavity 30 formed at the upper end of a block 23 which carried the upper end of a divergent yarn passageway 24 communication with cavity 30 and is positioned within the casing 15 by means of a tubular spacer 25 retained in the casing by screws 26. The lower and major part of passageway 24 which protrudes from the lower end of casing 15, is supported by brackets 27 attached to casing 15 and is surrounded by heating means (not shown). A small groove 28 in the top of block 23 allows a pressure or other measuring instrument to be attached through a tapping 29 in the casing 15.

In operation compressed fluid entering holes 18 passes through the diffusing plate 21 into cavity 30 and thence into passageway 24 thereby inducing a suction in tube 19 which draws in a yarn (not shown) tensioning it within the tube 19 and forwarding it through passage 24 at a reducing fluid velocity and under increasing relaxation conditions. The relaxed yarn leating the lower end of passage 24 may be taken up and collected into a package as in the foregoing description. The examples which follow illustrate the invention and the manner in which it may be performed. In these Examples where intrinsic viscosity is mentioned this has been measured in solution in o-chlorophenol at 25C and retraction under load is measured as follows.

A hank of the specimen filament or yarn, made by taking ten 1.1 meter wraps on a wrap wheel, is suspended for 2 minutes in boiling water under a load of 0.003 g. per denier and the shrunk length (L,) measured first under this same load of 0.003 g. per denier then under a load of 0.3 g. per denier (L which is sufficient to decrimp the specimen. The retraction under load is then expressed as An alternative measure of the relaxing effect is the percentage crimp taking place in the relax zone which may be calculated from the relax ratio and the measured linear shrinkage (which does not include shrinkage due to crimping) from the following relationship.

% crimp= l [l/(l -0.01.S)R]100 where S is the percent shrinkage and R is the relax ratio.

EXAMPLE 1 A l40-denier filamentary yarn of 30 conjugate filaments consisting of equal parts of two ethylene terephthalate polymers arranged in side-by-side fashion, the polymers differing only in having intrinsic viscosities of 0.67 and 0.47, is drawn from the draw roll of a drawing machine at 380 meters per minute by a simple air ejector supplied with compressed air at ambient temperature, 20C, and a pressure of l.7kg/cm From the exit of the ejector yarn is forwarded directly into a coaxial tube of larger diameter (6 cm.) which is heated to an internal air temperature of 180C. by means of an external electrical resistance heater encircling and in close contact with the walls. Some ambient air is drawn into the ejector with the yarn and the combined flow rate is 0.9 cubic meters per hour (measured at S.T.P., i.e., 15C. and 760 mm. Hg). Air leaving the ejector drops rapidly in pressure and the yarn carried with it relaxes due to the drop in tension and the effect of heat in the relaxation tube. The relax tube length is 45 cm and the maximum operable relax ratio is 1.6 from which the percent crimp in the relax zone is 25 percent. The yarn emerging from the relax zone passes through a nip roll and is wound up by a conventional ring and traveler winding means.

EXAMPLE 2 An 18 denier single conjugate filament yarn consisting of equal parts of two polyamides arranged in sideby-side fashion, the polymers being polyhexamethylene adipamide and a copolymer derived from hexamethylene diammonium adipate, epsilon caprolactam and hexamethylene diammonium isophthalate in the proportions :10:10 by weight, is treated as in the foregoing Example at a relax ratio of 2.0 to produce a crimped yarn.

EXAMPLES 3-4 Yarn as used in Example 1 is relaxed in the same apparatus under the same conditions except that higher a heating zone temperature of 250C and two lower values of relax ratio are used producing crimped products of improved bulk as shown below;

Example Relax ratio Retraction under load In COMPARATIVE EXAMPLE Yarn as used in Example 1 is relaxed as in that example with the exception that compressed air supplied to the ejector is heated to 300C. The maximum runnable relax ratio under these conditions is only 1.4 from which the percentage crimp in the relax zone is calculated as 16 percent.

What is claimed is:

l. A process for relaxing a running continuous filamentary yarn composed of thermoplastic polymeric material, wherein the yarn is entrained in and tensioned by a stream of unheated gas passing therewith into a heated enclosure wherein it is caused to assume a helical or zigzag path out of contact with any solid part of the enclosure and wherein the gas pressure falls together with the tension in the yarn.

2. A process according to claim 1 wherein the enclosure is heated with a counter-current flow of heated gas.

3. A process according to claim 1 wherein the enclosure is heated with a cocurrent flow of heated gas.

4. A process according to claim 1 wherein the enclosure is heated by electrically heating the walls of the enclosure.

5. A process according to claim 1 wherein the yarn has an inherent retraction tendancy in the unrelaxed state.

6. Process according to claim 5 wherein the yarn comprises conjugate filaments with the components arranged in side-by-side fashion.

7. Process according to claim 5 wherein the yarn comprises filaments which have been asymmetrically heated.

8. Process as in claim 5 wherein the yarn comprises conjugate filaments with the components arranged in eccentric sheath-core fashion.

9. Process as in claim 5 wherein the yarn comprises filaments which have been asymmetrically cooled.

10. Process as in claim 5 wherein the yarn comprises filaments which have been false twisted.

11. A process according to claim 1 wherein the heating zone has a temperature of l80250C.

12. A process according to claim 1 wherein the thermoplastic polymeric material is selected from the group consisting of polyesters, polyamides, polyolefines, and copoloymers within and between these classes.

13. A process for relaxing a running continuous filamentary yarn of thermoplastic polymeric material comprising: entraining the yarn in and tensioning it by a pressurized stream of unheated gas; passing the yarn and stream of unheated gas into one end of a heated tubular enclosure of relatively large cross section to thereby expand the stream and decrease the tension in the yarn; moving the yarn in a helical or zigzag path through and relative to the enclosure; and withdrawing the relaxes yarn from the opposite end of the enclosure.

14. A process as in claim 13 wherein the yarn enters the enclosure through a rotating or oscillating passageway to thereby produce said helical or zigzag path.

Claims

1. A process for relaxing a running continuous filamentary yarn composed of thermoplastic polymeric material, wherein the yarn is entrained in and tensioned by a stream of unheated gas passing therewith into a heated enclosure wherein it is caused to assume a helical or zigzag path out of contact with any solid part of the enclosure and wherein the gas pressure falls together with the tension in the yarn.

3. A process according to claim 1 wherein the enclosure is heated with a co-current flow of heated gas.

11. A process according to claim 1 wherein the heating zone has a temperature of 180*-250*C.